In the field of printed content management, it is often desirable to be able to define a persistent coordinate system over a printed document, the coordinate system being physically imprinted on the document through printing or some similar process. Provided the coordinate system is consistent throughout the lifetime of the document, it may be used to uniquely identify and reference areas on the document, which are, from a security or document workflow point of view, of particular importance.
This coordinate system is usually represented using a two-dimensional (2D) barcode, that is printed on the document using ink or toner. By combining coordinate system information in the barcode with information about the location and type of regions of importance on the document, the document can be considered self-contained, thereby permitting the document to be processed without referring to a central source of information. Such a document has application in numerous areas, including document access control, workflow processing and document verification.
It is particularly desirable that the physical representation of the coordinate system on the document does not interfere with the actual content of the document. In the case that the physical representation is printed on the document using ink or toner, it is preferable that the representation have low-visibility, or even be invisible, for example formed using infrared ink or the like.
One method for generating such a self-contained document involves encoding a tiled maximum length code in a 2D barcode across the surface of the document. The coordinates of each information carrying indicia on the barcode may be calculated by observing the offset of codes in adjacent columns of indicia. The coordinates are implicitly encoded in the offset between columns. Provided the maximum length code is known to both the encoder and the decoder, the coordinate system can be recovered. Arbitrary data can then be encoded by allotting a number of the indicia for this purpose, with coordinate system data and arbitrary data being interleaved across the page.
Another method for generating such a self-contained document consists of encoding a pseudo-random sequence in a 2D barcode encoded across the face of the document. On decoding, provided the decoder knows the pseudo-random sequence encoded in the barcode, for example by knowing the seed from which the pseudo-random sequence was generated, and the pseudo-random sequence does not repeat within the document, then the position of each encoded value in the sequence provides a coordinate system by which to address the document. Like the previously mentioned method, arbitrary data may also be encoded by interleaving arbitrary data with the coordinate data.